Multiplexer

ABSTRACT

Four frequency components (f 1  to f 4 ) (where, f 1&lt; f 2&lt; f 3&lt; f 4 ) are input into a port ( 10 ) of a first demultiplexing filter circuit ( 1 ), and demultiplexed into low frequency components (f 1  and f 2 ) and high frequency components (f 3  and f 4 ), and input in a port ( 20 ) of a second demultiplexing filter circuit ( 2 ) and a port ( 30 ) of a third demultiplexing filter circuit ( 3 ), respectively. The frequency components (f 1  and f 2 ) are demultiplexed into the component (f 1 ) and the component (f 2 ) by the second demultiplexing filter circuit ( 2 ), and output from a port ( 23 ) and a port ( 24 ), respectively. The frequency components (f 3  and f 4 ) are demultiplexed into the component (f 3 ) and the component (f 4 ) by the third demultiplexing filter circuit ( 3 ), and output from a port ( 33 ) and a port ( 34 ), respectively. The first demultiplexing filter circuit ( 1 ) comprises a low-pass filter ( 11 ) and a high-pass filter ( 12 ), the second demultiplexing filter circuit ( 2 ) comprises a low-pass filter ( 21 ) and a combined filter ( 22 ) of a combination of a low-pass filter and a band elimination filter, and the third demultiplexing filter circuit ( 3 ) comprises a combined filter ( 31 ) of a combination of a high-pass filter and a band elimination filter and a high-pass filter ( 32 ). These demultiplexing filter circuits are formed of a stacked structure.

TECHNICAL FIELD

[0001] The present invention relates to a multiplexer used for a mobilecommunication device such as a portable terminal of a cellular phonesystem.

BACKGROUND ART

[0002] Popularization of the cellular phone system has been spectacularin recent years, and improvements have been pursued in functions of theportable terminal used in the cellular phone system. As one of suchimprovements, a cellular phone system has been presented, which uses adual band portable terminal to enable communications in two frequencybands at one portable terminal. Further, a cellular phone system hasbeen presented, which uses a multifunctional portable terminal based onpositioning by a global positioning system (GPS), an addition of a bluetooth (BT) etc. To configure this multifunctional cellular phone system,a function of selecting its four frequency bands becomes necessary.Besides, in order to realize such a function, a compact multiplexer isrequired for use in the portable terminal. Separation of the fourfrequency bands can be realized by cascade-connecting three diplexers.FIG. 17 shows a block diagram of such a conventional demultiplexingfilter circuit element.

[0003] In the demultiplexing filter circuit element of FIG. 17, threedemultiplexing filter circuits each constituted of a low-pass filter(LPF) and a high-pass filter (HPF) are connected in series as shown.Frequency pass bands of the demultiplexing filter circuits are differentfrom one another. For example, when RF signals or frequency components(hereinafter, RF signals are carriers and signals in the frequencybands) f1 to f4 (frequency band of f1<frequency band of f2<frequencyband of f3<frequency band of f4) included in the respective fourfrequency bands are input to the first demultiplexing filter circuit,the frequency component f1 is output from an output port of the low-passfilter side, and the remaining RF signals f2 to f4 are output from anoutput port of the high-pass filter side. The RF signals f2 to f4 areinput to the second demultiplexing filter circuit. Here, the RF signalf2 is output from an output port of the low-pass filter side, and theremaining RF signals f3 and f4 are output from an output port of thehigh-pass filter side. The RF signals f3 and f4 are input to the thirddemultiplexing filter circuit. Here, the RF signal f3 is output from anoutput port of the low-pass filter side, and the RF signal f4 is outputfrom an output port of the high-pass filter side.

[0004] However, in the aforementioned demultiplexing filter circuitwhere the three demultiplexing filter circuits are cascade-connected,while the four frequency bands can be separated as described above,there are some problems described below.

[0005] First, the RF signals f3 and f4 are passed through the threedemultiplexing filter circuits, creating a problem of a large insertionloss in signal. Especially, when weak radio waves are dealt with as inthe case of the GPS, it is necessary to reduce insertion losses as muchas possible. Thus, a large insertion loss poses a serious problem. Inthe case of simply using three normal individual demultiplexing filterelements and connecting the elements, element dimensions are increasedto interfere with miniaturization. Furthermore, if a plurality offrequency bands are close to one another, there is a problem ofinsufficient separation of RF signals.

DISCLOSURE OF THE INVENTION

[0006] In view of the foregoing, an object of the present invention isto provide a compact and high-performance multiplexer which enablesfurther miniaturization, a reduction of insertion losses and a furtherimprovement of isolation characteristics.

[0007] In order to accomplish the above object, according to the presentinvention, there is provided a multiplexer comprising: a firstdemultiplexing filter circuit for separating or demultiplexing afrequency band including a first RF signal f1, a second RF signal f2, athird RF signal f3 and a fourth RF signal f4 different from one another(where f1<f2<f3<f4) into a frequency band which includes the f1 and thef2 but neither of the f3 and the f4 practically, and a frequency bandwhich includes the f3 and the f4 but neither of the f1 and the f2practically; a second demultiplexing filter circuit for separating thefrequency band including the f1 and the f2 which is obtained by theseparation of the first demultiplexing filter circuit into a frequencyband which includes the f1 but none of the f2 to the f4 practically, anda frequency band which includes the f2 but none of the f1, the f3 andthe f4 practically; and a third demultiplexing filter circuit forseparating the frequency band including the f3 and the f4 which isobtained by the separation of the first demultiplexing filter circuitinto a frequency band which includes the f3 but none of the f1, the f2and the f4 practically, and a frequency band which includes the f4 butnone of the f1 to the f3 practically,

[0008] wherein the second demultiplexing filter circuit comprises afilter of combination of low-pass and band elimination filters or a bandpass filter as a filter where the frequency band including the f2 butnone of the f1, the f3 and the f4 practically is set to be a pass band,and the third demultiplexing filter circuit comprises a filter ofcombination of high-pass and band elimination filters or a band passfilter as a filter where the frequency band including the f3 but none ofthe f1, the f2 and the f4 practically is set to be a pass band.

[0009] According to the present invention, “not including the RFsignal(s) practically” means that the RF signals are attenuated torequired amounts from the standpoint of achieving the separationpurpose. It does not necessarily mean complete elimination of the RFsignal(s).

[0010] In one embodiment of the present invention, the firstdemultiplexing filter circuit comprises a low-pass filter as a filterwhere the frequency band including the f1 and the f2 but neither of thef3 and the f4 practically is set to be a pass band, and a high-passfilter as a filter where the frequency band including the f3 and the f4but neither of the f1 and the f2 practically is set to be a pass band.In another embodiment of the present invention, the seconddemultiplexing filter circuit comprises a low-pass filter as a filterwhere the frequency band including the f1 but none of the f2 to the f4practically is set to be a pass band, and the third demultiplexingfilter circuit comprises a high-pass filter as a filter where thefrequency band including the f4 but none of the f1 to the f3 practicallyis set to be a pass band.

[0011] In still another embodiment of the present invention, themultiplexer is formed of a laminated or stacked structural body, thelaminated structural body is constituted so as to include a plurality ofinsulating layers and a patterned conductive layer arranged between theinsulating layers, each of the first demultiplexing filter circuit, thesecond demultiplexing filter circuit and the third demultiplexing filtercircuit includes an inductance component and a capacitance component,and the inductance component and the capacitance component are formed byusing the patterned conductive layer. The insulating layers are made of,for example, ceramics, and the patterned conductive layer is made of,for example, metal.

[0012] The multiplexer of the present invention has the combined threedemultiplexing filter circuits, and the input of the RF signals f1 to f4(where f1<f2<f3<f4) belonging to the four frequency bands different fromone another is separated into the RF signals f1 and f2 of the lowerfrequency bands and the RF signals of f3 and f4 of the higher frequencybands by the first demultiplexing filter circuit, the RF signals f1 andf2 of the lower frequency bands output from the first demultiplexingfilter circuit are separated into the RF signal f1 and the RF signal f2by the second demultiplexing filter circuit, and the RF signals f3 andf4 of the higher frequency bands output from the first demultiplexingfilter circuit are separated into the RF signal f3 and the RF signal f4by the third demultiplexing filter circuit. By this structure, thenumber of stages of cascade-connected demultiplexing filter circuits canbe reduced to two, thereby achieving a reduction of insertion losses.Further, the first demultiplexing filter circuit may comprise thelow-pass filter and the high-pass filter, the second demultiplexingfilter circuit may comprise the low-pass filter for passing the RFsignal f1 and the filter of the combination of low-pass and bandelimination filters for taking out the RF signal f2, and the thirddemultiplexing filter circuit may comprise the high-pass filter forpassing the RF signal f4 and the filter of the combination of high-passand band elimination filters for taking out the RF signal f3. Thus,isolation characteristics of each RF signal can be improved, the numberof notch circuits can be reduced, and an attenuation load of eachdemultiplexing filter circuit can be reduced. By forming thesedemultiplexing filter circuits into one laminated structural body, acompact and high-performance multiplexer which has small insertionlosses and improved isolation characteristics is provided.

[0013] Further, also by using a band-pass filter in place of thecombination filter including the band elimination filter in each of thesecond demultiplexing filter circuit and the third demultiplexing filtercircuit, a high-performance multiplexer having similar effects isprovided.

[0014] The description of the multiplexer has been made with referenceto the case where the mixed RF signal of f1 to f4 is input from thefirst demultiplexing filter circuit side. However, the multiplexer ofthe present invention has a function of reversing a signal flow fromthat of the foregoing, inputting individual RF signals from the secondand third demultiplexing filter circuits side, and outputting the mixedRF signal of f1 to f4 from the first demultiplexing filter circuit side.

[0015] As the four RF signals, there is an example of a combination ofRF signals for a global system for mobile communications (GSM: 800 MHzband) as f1, a global positioning system (GPS: 1.5 GHz band) as f2, adigital communication system (DCS: 1.8 GHz band) as f3, and a blue tooth(BT: 2.4 GHz band) as f4.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram of a multiplexer of the presentinvention.

[0017]FIG. 2 is a constitutional diagram of a first demultiplexingfilter circuit in the multiplexer of FIG. 1.

[0018]FIG. 3 is a diagram showing frequency characteristics of the firstdemultiplexing filter circuit in the multiplexer of FIG. 1.

[0019]FIG. 4 is a constitutional diagram of a second demultiplexingfilter circuit in the multiplexer of FIG. 1.

[0020]FIG. 5 is a diagram showing frequency characteristics of thesecond demultiplexing filter circuit in the multiplexer of FIG. 1.

[0021]FIG. 6 is a constitutional diagram of a third demultiplexingfilter circuit in the multiplexer of FIG. 1.

[0022]FIG. 7 is a diagram showing frequency characteristics of the thirddemultiplexing filter circuit in the multiplexer of FIG. 1.

[0023]FIG. 8 is an exploded perspective view showing a laminated orstacked structure of the multiplexer of FIG. 1.

[0024]FIG. 9 is a perspective view of a laminated structural body of themultiplexer of FIG. 1.

[0025]FIG. 10 is a block diagram of a multiplexer of the presentinvention.

[0026]FIG. 11 is a constitutional diagram of a second demultiplexingfilter circuit in the multiplexer of FIG. 10.

[0027]FIG. 12 is a diagram showing frequency characteristics of thesecond demultiplexing filter circuit in the multiplexer of FIG. 10.

[0028]FIG. 13 is a constitutional diagram of a third demultiplexingfilter circuit in the multiplexer of FIG. 10.

[0029]FIG. 14 is a diagram showing frequency characteristics of thethird demultiplexing filter circuit in the multiplexer of FIG. 10.

[0030]FIG. 15 is an exploded perspective view showing a laminatedstructure of the multiplexer of FIG. 10.

[0031]FIG. 16 is a perspective view of a laminated structural body ofthe multiplexer of FIG. 10.

[0032]FIG. 17 is a block diagram of a conventional demultiplexing filtercircuit element.

BEST MODES FOR CARRYING OUT THE INVENTION

[0033] Next, the embodiments of the present invention will be describedwith reference to the accompanying drawings.

[0034]FIG. 1 shows a circuitry block diagram of a first embodiment ofthe present invention. A multiplexer of the first embodiment comprises afirst demultiplexing filter circuit 1, a second demultiplexing filtercircuit 2 and a third demultiplexing filter circuit 3, and an inputincluding first to fourth frequency bands different from one another(frequency band of f1<frequency band of f2<frequency band off3<frequency band of f4) which include the respective first to fourth RFsignals or frequency components f1 to f4 different from one another(where f1<f2<f3<f4) is entered to an input/output port 10 of the firstdemultiplexing filter circuit 1. An output including the frequency bandof f1 and the frequency band of f2 is obtained from an input/output port13 of the first demultiplexing filter circuit 1, which is then input toan input/output port 20 of the second demultiplexing filter circuit 2.On the other hand, an output including the frequency band of f3 and thefrequency band of f4 is obtained from an input/output port 14 of thefirst demultiplexing filter circuit 1, which is then input to aninput/output port 30 of the third demultiplexing filter circuit 3.Outputs of the frequency bands of f1, f2 are obtained from therespective input/output ports 23, 24 of the second demultiplexing filtercircuit 2, and outputs of the frequency bands of f3, f4 are obtainedfrom the respective input/output ports. 33, 34 of the thirddemultiplexing filter circuit 3.

[0035] The first demultiplexing filter circuit 1 includes a first filter11 and a second filter 12. The first filter 11 is constituted of alow-pass filter LPF where a band including the f1 and the f2 but neitherof the f3 and the f4 practically is a pass band, and the second filter12 is constituted of a high-pass filter HPF where a band including thef3 and the f4 but neither of the f1 and the f2 practically is a passband. One input/output port of the first filter 11 and the second filter12 is set as a common port 10.

[0036] The second demultiplexing filter circuit 2 includes a thirdfilter 21 and a fourth filter 22. The third filter 21 is constituted ofa low-pass filter LPF where a band including the f1 but none of the f2to the f4 practically is a pass band, and the fourth filter 22 is afilter where a band including the f2 but none of the f1, the f3 and thef4 practically is a pass band, and constituted of a filter ofcombination of a low-pass filter LPF and a band elimination filter BEF.One input/output port of the third filter 21 and the fourth filter 22 isset as a common port 20. The common port 20 is connected to aninput/output port 13 of the first filter 11 which is not a common port.

[0037] The third demultiplexing filter circuit 3 includes a fifth filter31 and a sixth filter 32. The fifth filter 31 is a filter where a bandincluding the f3 but none of the f1, the f2 and the f4 practically is apass band, and constituted of a filter of combination of a high-passfilter HPF and a band elimination filter BEF, and the sixth filter 32 isconstituted of a high-pass filter HPF where a band including the f4 butnone of the f1 to the f3 practically is a pass band. One input/outputport of the fifth filter 31 and the sixth filter 32 is set as a commonport 30. The common port 30 is connected to an input/output port 14 ofthe second filter 12 which is not a common port.

[0038]FIG. 2 shows a constitutional diagram of the first demultiplexingfilter circuit 1. The first demultiplexing filter circuit 1 comprises alow-pass filter 11 including an inductance component L11 and capacitancecomponents C11, C12, and a high-pass filter 12 including an inductancecomponent L12 and capacitance components C13, C14. For the RF signals f1to f4 input from the common port 10, the low-pass filter 11 operates tooutput only the RF signals f1 and f2 of the lower frequency bands to theinput/output port 13 of the low-pass filter 11, and the high-pass filter12 operates to output only the RF signals f3 and f4 of the higherfrequency bands to the input/output port 14 of the high-pass filter 12.

[0039]FIG. 3 is a frequency characteristic diagram of the firstdemultiplexing filter circuit 1, especially the low-pass filter 11 andthe high-pass filter 12 constituting the circuit. Here, a change of anattenuation amount ATTN with respect to a frequency FREQ is shown.

[0040]FIG. 4 shows a constitutional diagram of the second demultiplexingfilter circuit 2. The second demultiplexing filter circuit 2 comprises alow-pass filter 21 including an inductance component L21 and capacitancecomponents C21, C22, and a filter 22 of combination of low-pass and bandelimination filters including inductance components L22, L23, L24 andcapacitance components C23, C24, C25, C26, C27, C28. For the RF signalsf1, f2 input from the common port 20, the low-pass filter 21 operates tooutput only the RF signal fl to the input/output port 23 of the low-passfilter 21, and the filter 22 of the combination of low-pass and bandelimination filters operates to output only the RF signal f2 to theinput/output port 24 of the combined filter 22.

[0041]FIG. 5 is a frequency characteristic diagram of the seconddemultiplexing filter circuit 2, especially the low-pass filter 21 andthe combination filter 22 constituting the circuit. Here, a change of anattenuation amount ATTN with respect to a frequency FREQ is shown. Inthe filter 22 of the combination of low-pass and band eliminationfilters, a non-pass band is formed in the band including the RF signalf1, and the RF signal f1 is eliminated nearly completely to take outonly the RF signal f2. In the combination filter 22, in a side of afrequency higher than the RF signal f2, attenuation characteristics bythe low-pass filter of the combination filter 22 are doubly applied inaddition to attenuation characteristics by the low-pass filter 11 of thefirst demultiplexing filter circuit 1. Thus, separation characteristicsof the RF signal f2 are good. Especially, in a place where a weak radiowave of a GPS or the like is conceivable as the RF signal f2, in thecase of passing and taking out such a weak radio wave, other RF signalsmust be eliminated as completely as possible, and a loss during passageis preferably small. Thus, the aforementioned constitution of the seconddemultiplexing filter circuit 2 is best suited for separation of theweak radio wave of the GPS or the like.

[0042]FIG. 6 shows a constitutional diagram of the third demultiplexingfilter circuit 3. The third demultiplexing filter circuit 3 comprises afilter 31 of combination of high-pass and band elimination filtersincluding inductance components L31, L32, L33 and capacitance componentsC31, C32, C33, C34, C35, C36, and a high-pass filter 32 including aninductance component L34 and capacitance components C37, C38. For the RFsignals f3, f4 input from the common port 30., the filter 31 of thecombination of high-pass and band elimination filters operates to outputonly the RF signal f3 to the input/output port 33 of the combinationfilter 31, and the high-pass filter 32 operates to output only the RFsignal f4 to the input/output port 34 of the high-pass filter 32.

[0043]FIG. 7 is a frequency characteristic diagram of the thirddemultiplexing filter circuit 3, especially the combination filter 31and the high-pass filter 32 constituting the circuit. Here, a change ofan attenuation amount ATTN with respect to a frequency FREQ is shown. Inthe filter 31 of the combination of high-pass and band eliminationfilters, a non-pass band is formed in the band including the RF signalf4, and the RF signal f4 is eliminated nearly completely to take outonly the RF signal f3. In the combination filter 31, in a side of afrequency lower than the RF signal f3, attenuation characteristics bythe high-pass filter of the combination filter 31 are doubly applied inaddition to attenuation characteristics by the high-pass filter 12 ofthe first demultiplexing filter circuit 1. Thus, separationcharacteristics of the RF signal f3 are good. Especially, in the case ofpassing and taking out a weak radio wave, other RF signals must beeliminated as completely as possible, and a loss during passage ispreferably small. Thus, the aforementioned constitution of the thirddemultiplexing filter circuit 3 is best suited for separation of a weakradio wave used as the RF signal f3.

[0044] The aforementioned multiplexer of the first embodiment ispreferably formed in a laminated or stacked structural body. That is,preferably, the inductance components L11, L12, L21 to L24, L31 to 34and the capacitance components C11 to C14, C21 to 28, C31 to 38 of thefirst demultiplexing filter circuit 1, the second demultiplexing filtercircuit 2 and the third demultiplexing filter circuit 3 are formed byusing patterned conductive layers constituting the laminated structuralbody.

[0045] A perspective view of such a laminated structural body is shownin FIG. 9, and an exploded perspective view thereof is shown in FIG. 8.The laminated structural body has external ground (GND) terminals 101,103, 104, 106, 108, 110, 112, an external input terminal 102, andexternal output terminals 105, 107, 109, 111, which are formed of thepatterned conductive layers.

[0046] This laminated structural body can be prepared by using a sheetlaminating method described below.

[0047] First, a ceramic green sheet is prepared. As the ceramic greensheet, a ceramic dielectric material which can be baked at a lowtemperature of 950° C. or lower is preferable. For example, a materialhaving a dielectric constant of 5 to 70, esp about 10, is used. Apredetermined number of such ceramic green sheets are laminated. On eachceramic green sheet, through-holes are formed in required positions whenneeded, and patterns (including a pattern by a conductor of silver (Ag)paste or the like filling the through-holes) are formed on a surface byusing a screen printing method to apply a metal paste such as Ag pasteor the like. The laminated body of the ceramic green sheets is bakedintegrally at about 900° C., and a conductive film (electrode) for theexternal GND terminal, a conductive film (electrode) for the externalinput terminal, and a conductive film (electrode) for the externaloutput terminal are formed on a top surface, a bottom surface and a sideface thereof, whereby a laminated structural body including aninsulating layer made of a ceramic dielectric material and a patternedconductive layer (may be referred to as “electrode”, hereinafter) madeof a conductor such as Ag or the like is obtained.

[0048] A thickness of the insulating layer is, for example, 0.02 to 0.3mm, and a thickness of the patterned conductive layer is, for example0.005 to 0.02 mm. A dimension of the laminated structural body is, forexample, 45 mm long×32 μmm wide×20 mm thick.

[0049] In FIG. 8, reference numerals 201 to 216 denote rectangularinsulating layers, reference numerals 113, 136, 157, 170, 179 denoteearth electrodes (patterned conductive layers for earths connected tothe external GND terminals), and these earth electrodes have drawerparts connected to the external GND terminals 101, 103, 104, 106, 108,110, 112. Reference numerals 114, 116, 118, 120, 121, 125, 140, 142,144, 150, 158, 165, 173, 176 denote coil electrodes (patternedconductive layers for forming the inductance components), and referencenumerals 123, 127, 129 to 132, 134, 135, 137 to 139, 146 to 148, 152 to155, 161, 162, 167, 168, 172 denote capacitance electrodes (patternedconductive layers for forming the capacitance components). Referencenumerals 115, 117, 119, 122, 124, 126, 128, 133, 141, 143, 145, 149,151, 156, 159, 160, 163, 164, 166, 169, 171, 174, 175, 177, 178 denoteconductive layers filling the through-holes, and these conductive layersconnect a plurality among the earth electrodes, the coil electrodes andthe capacitance electrodes.

[0050] Hereinafter, a constitution of the laminated structural bodyshown in FIG. 8 will be described corresponding to the constitutions ofthe demultiplexing filter circuits 1, 2, 3 shown in FIGS. 2, 4 and 6.

[0051] Regarding the low-pass filter 11 of FIG. 2, the capacitancecomponent C11 comprises the capacitance electrode 137 and the earthelectrode 136. The capacitance component C12 comprises the capacitanceelectrode 138 and the earth electrode 136. One end of the capacitanceelectrode 138 is connected to the external input terminal 102. Theinductance component L11 comprises the coil electrode 144, thethroughhole 151 and the coil electrode 150. One end of the coilelectrode 150 is connected to the external input terminal 102.

[0052] Regarding the high-pass filter 12 of FIG. 2, the capacitancecomponent C13 comprises the capacitance electrode 129 and thecapacitance electrode 123. One end of the capacitance electrode 129 isconnected to the external input terminal 102. The capacitance componentC14 comprises the capacitance electrode 130 and the capacitanceelectrode 123. The inductance component L12 comprises the through-hole124, the coil electrode 118, the through-hole 119, the coil electrode114 and the through-hole 115.

[0053] Regarding the low-pass filter 21 of FIG. 4, the capacitancecomponent C21 comprises the capacitance electrode 131 and the earthelectrode 136. One end of the capacitance electrode 131 is connected tothe external output terminal 105. The capacitance component C22comprises the capacitance electrode 132 and the earth electrode 136. Theinductance component L21 comprises the through-hole 141, the coilelectrode 120, the through-hole 126, the coil electrode 125 and thethrough-hole 133.

[0054] Regarding the filter 22 of the combination of low-pass and bandelimination filters of FIG. 4, the capacitance component C23 comprisesthe capacitance electrode 139 and the earth electrode 136. Thecapacitance component C24 comprises the capacitance electrode 172 andthe earth electrode 170. One end of the capacitance electrode 172 isconnected to the external output terminal 107. The inductance componentL22 comprises the coil electrode 140. One end of the coil electrode 140is connected to the external output terminal 107. The capacitancecomponent C25 comprises the capacitance electrode 147 and thecapacitance electrode 153. The capacitance component C27 comprises thecapacitance electrode 153 and the earth electrode 157. The inductancecomponent L23 comprises the through-hole 159, the coil electrode 158 andthe through-hole 160. The capacitance component C26 comprises thecapacitance electrode 146 and the capacitance electrode 152. One end ofthe capacitance electrode 146 is connected to the external outputterminal 107. The capacitance component C28 comprises the capacitanceelectrode 152 and the earth electrode 157. The inductance component L24comprises the through-hole 166, the coil electrode 165 and thethrough-hole 171.

[0055] Regarding the filter 31 of the combination of high-pass and bandelimination filters of FIG. 6, the capacitance component C33 comprisesthe capacitance electrode 155 and the capacitance electrode 148. One endof the capacitance electrode 155 is connected to the external outputterminal 109. The inductance component L33 comprises the through-hole149, the coil electrode 142, and the through-hole 143. The capacitancecomponent C34 comprises the capacitance electrode 154 and thecapacitance electrode 148. The capacitance component C32 comprises thecapacitance electrode 162 and the capacitance electrode 168. Thecapacitance component C31 comprises the capacitance electrode 168 andthe earth electrode 170. The inductance component L31 comprises thethrough-hole 177, the coil electrode 176 and the throughhole 178. Thecapacitance component C35 comprises the capacitance electrode 161 andthe capacitance electrode 167. The capacitance component C36 comprisesthe capacitance electrode 167 and the earth electrode 170. Theinductance component L32 comprises the through-hole 174, the coilelectrode 173 and the through-hole 175.

[0056] Regarding the high-pass filter 32 of FIG. 6, the capacitancecomponent C37 comprises the capacitance electrode 134 and thecapacitance electrode 127. The inductance component L34 comprises thethrough-hole 128, the coil electrode 121, the through-hole 122, the coilelectrode 116 and the through-hole 117. The capacitance component C38comprises the capacitance electrode 135 and the capacitance electrode127. One end of the capacitance electrode 135 is connected to theexternal output terminal 111.

[0057] As described above, according to the first embodiment, it ispossible to obtain the high-performance multiplexer where insertionlosses are small, isolation characteristics are improved more, and thefour RF signals are separated into the respective components. Moreover,according to the embodiment, the form of the laminated structural bodyenables sufficient miniaturization.

[0058] Next, description will be made of a multiplexer which uses bandpass filters in place of the band elimination filters used in the seconddemultiplexing filter circuit 2 and the third demultiplexing filtercircuit 3 in the circuitry of the first embodiment as a secondembodiment.

[0059]FIG. 10 shows a circuitry block diagram of the second embodiment.The multiplexer of the second embodiment comprises a firstdemultiplexing filter circuit 4, a second demultiplexing filter circuit5 and a third demultiplexing filter circuit 6. As in the case of thefirst embodiment, an input including first to fourth frequency bandsdifferent from one another which include the respective first to fourthRF signals f1 to f4 different from one another is entered to aninput/output port 40 of the first demultiplexing filter circuit 4. Anoutput including the frequency band of f1 and the frequency band of f2is obtained from an input/output port 43 of the first demultiplexingfilter circuit 4, which is then input to an input/output port 50 of thesecond demultiplexing filter circuit 5. On the other hand, an outputincluding the frequency band of f3 and the frequency band of f4 isobtained from an input/output port 44 of the first demultiplexing filtercircuit 4, which is then input to an input/output port 60 of the thirddemultiplexing filter circuit 6. Outputs of the frequency bands of f1,f2 are obtained from the respective input/output ports 53, 54 of thesecond demultiplexing filter circuit 5, and outputs of the frequencybands of f3, f4 are obtained from the respective input/output ports 63,64 of the third demultiplexing filter circuit 6.

[0060] The first demultiplexing filter circuit 4 includes a first filter41 and a second filter 42. The first filter 41 is constituted of alow-pass filter LPF where a band including the f1 and the f2 but neitherof the f3 and the f4 practically is a pass band, and the second filter42 is constituted of a high-pass filter HPF where a band including thef3 and the f4 but neither of the f1 and the f2 practically is a passband. One input/output port of the first filter 41 and the second filter42 is set as a common port 40. A constitution of this firstdemultiplexing filter circuit 4 is similar to that of the firstdemultiplexing filter circuit 1 of the first embodiment.

[0061] The second demultiplexing filter circuit 5 includes a thirdfilter 51 and a fourth filter 52. The third filter 51 is constituted ofa low-pass filter LPF where a band including the f1 but none of the f2to the f4 practically is a pass band, and the fourth filter 52 is afilter where a band including the f2 but none of the f1, the f3 and thef4 practically is a pass band, and constituted of a band pass filterBPF. One input/output port of the third filter 51 and the fourth filter52 is set as a common port 50. The common port 50 is connected to aninput/output port 43 of the first filter 41 which is not a common port.

[0062] The third demultiplexing filter circuit 6 includes a fifth filter61 and a sixth filter 62. The fifth filter 61 is a filter where a bandincluding the f3 but none of the f1, the f2 and the f4 practically is apass band, and constituted of a band pass filter BPF, and the sixthfilter 62 is constituted of a high-pass filter HPF where a bandincluding the f4 but none of the f1 to the f3 practically is a passband. One input/output port of the fifth filter 61 and the sixth filter62 is set as a common port 60. The common port 60 is connected to aninput/output port 44 of the second filter 42 which is not a common port.

[0063]FIG. 11 shows a constitutional diagram of the seconddemultiplexing filter circuit 5. The second demultiplexing filtercircuit 5 comprises a low-pass filter 51 including an inductancecomponent and a capacitance component, and a band pass filter 52including an inductance component and a capacitance component. For theRF signals f1, f2 input from the common port 50, the low-pass filter 51operates to output only the RF signal f1 to the input/output port 53 ofthe low-pass filter 51, and the band pass filter 52 operates to outputonly the RF signal f2 to the input/output port 54 of the band passfilter 52.

[0064]FIG. 12 is a frequency characteristic diagram of the seconddemultiplexing filter circuit 5, especially the low-pass filter 51 andthe band pass filter 52 constituting the circuit. Here, a change of anattenuation amount ATTN with respect to a frequency FREQ is shown. Inthe band pass filter 52, the RF signal f1 is separated and eliminated totake out only the RF signal f2. In the band pass filter 52, in a side ofa frequency higher than the RF signal f2, attenuation characteristics bythe band pass filter 52 are doubly applied in addition to attenuationcharacteristics by the low-pass filter 41 of the first demultiplexingfilter circuit 4. Thus, separation characteristics of the RF signal f2are good. Especially, in a place where a weak radio wave of a GPS or thelike is conceivable as the RF signal f2, in the case of passing andtaking out such a weak radio wave, other RF signals must be eliminatedas completely as possible, and a loss during passage is preferablysmall. Thus, the aforementioned constitution of the seconddemultiplexing filter circuit 5 is best suited for separation of theweak radio wave of the GPS or the like.

[0065]FIG. 13 shows a constitutional diagram of the third demultiplexingfilter circuit 6. The third demultiplexing filter circuit 6 comprises aband pass filter 61 including an inductance component and a capacitancecomponent, and a high-pass filter 62 including an inductance componentand a capacitance component. For the RF signals f3, f4 input from thecommon port 60, the band pass filter 61 operates to output only the RFsignal f3 to the input/output port 63 of the band pass filter 61, andthe high-pass filter 62 operates to output only the RF signal f4 to theinput/output port 64 of the high-pass filter 62.

[0066]FIG. 14 is a frequency characteristic diagram of the thirddemultiplexing filter circuit 6, especially the band pass filter 61 andthe high-pass filter 62 constituting the circuit. Here, a change of anattenuation amount ATTN with respect to a frequency FREQ is shown. Inthe band pass filter 61, the RF signal f4 is separated and eliminated totake out only the RF signal f3. In the band pass filter 61, in a side ofa frequency lower than the RF signal f3, attenuation characteristics bythe band pass filter 61 are doubly applied in addition to attenuationcharacteristics by the high-pass filter 42 of the first demultiplexingfilter circuit 4. Thus, separation characteristics of the RF signal f3are good. Especially, in the case of passing and taking out a weak radiowave, other RF signals must be eliminated as completely as possible, anda loss during passage is preferably small. Thus, the aforementionedconstitution of the third demultiplexing filter circuit 6 is best suitedfor separation of a weak radio wave used as the RF signal f3.

[0067] The aforementioned multiplexer of the second embodiment ispreferably formed in a laminated structural body as in the case of thefirst embodiment. That is, preferably, the inductance components and thecapacitance components of the first demultiplexing filter circuit 4, thesecond demultiplexing filter circuit 5 and the third demultiplexingfilter circuit 6 are formed by using patterned conductive layersconstituting the laminated structural body.

[0068] A perspective view of such a laminated structural body is shownin FIG. 16, and an exploded perspective view thereof is shown in FIG.15. The laminated structural body has external ground (GND) terminals301, 303, 304, 306, 308, 310, 312, an external input terminal 302, andexternal output terminals 305, 307, 309, 311, which are formed of thepatterned conductive layers. A manufacturing method of this laminatedstructural body is similar to that described above with reference to thefirst equipment, and thus description thereof will be omitted.

[0069] In FIG. 15, reference numerals 401 to 414 denote rectangularinsulating layers, reference numerals 313, 335, 363, 374 denote earthelectrodes, and these earth electrodes have drawer parts connected tothe external GND terminals 301, 303, 304, 306, 308, 310, 312. Referencenumerals 314, 316, 318, 320, 321, 325, 346, 357, 364, 367, 370, 372denote coil electrodes (patterned conductive layers for forming theinductance components), and reference numerals 323, 327, 329 to 331,333, 334, 336 to 339, 341 to 343, 345, 348 to 350, 352, 353, 356, 359 to362 denote capacitance electrodes (patterned conductive layers forforming the capacitance components). Reference numerals 315, 317, 319,322, 324, 326, 328, 332, 340, 344, 347, 351, 354, 358, 365, 366, 368,369, 371, 373, 375, 376 denote conductive layers filling thethrough-holes, and these conductive layers connect a plurality among theearth electrodes, the coil electrodes and the capacitance electrodes.

[0070] Though not described in detail here, a proper combination of theearth electrodes, the coil electrodes, the capacitance electrodes andthe conductive layers in the through-holes enables formation ofinductance components, capacitance components and connections thereof.

[0071] As described above, also according to the second embodiment, itis possible to obtain the high-performance multiplexer where sufficientminiaturization is possible, insertion losses are small, isolationcharacteristics are improved more, and the four RF signals are separatedinto the respective components.

[0072] In the second embodiment, the band pass filters are used in placeof both of the combination filters including the band eliminationfilters used in the second demultiplexing filter circuit 2 and the thirddemultiplexing filter circuit 3 of the circuitry of the firstembodiment. However, according to the present invention, the band passfilter may be used in place of only one of the combined filtersincluding the band elimination filters used in the second demultiplexingfilter circuit 2 and the third demultiplexing filter circuit 3 of thecircuitry of the first embodiment. Also by this way, it is possible toobtain effects similar to those of the first embodiment and the secondembodiment.

INDUSTRIAL APPLICABILITY

[0073] As described above, according to the present invention, themultiplexer for separating signals belonging to the four frequency bandsincluding a weak radio wave of the GPS or the like well can beconstituted of a simple circuit, and an insertion loss of the weak radiowave of the GPS or the like can be reduced to improve a degree ofseparation from other radio waves. Moreover, by constituting the circuitof a laminated structure, it is possible to provide the multiplexerwhich is compact and excellent in separation performance.

1. A multiplexer comprising: a first demultiplexing filter circuit forseparating a frequency band including a first RF signal f1, a second RFsignal f2, a third RF signal f3 and a fourth RF signal f4 different fromone another (where f1<f2<f3<f4) into a frequency band which includes thef1 and the f2 but neither of the f3 and the f4 practically, and afrequency band which includes the f3 and the f4 but neither of the f1and the f2 practically; a second demultiplexing filter circuit forseparating the frequency band including the f1 and the f2 which isobtained by the separation of the first demultiplexing filter circuitinto a frequency band which includes the f1 but none of the f2 to the f4practically, and a frequency band which includes the f2 but none of thef1, the f3 and the f4 practically; and a third demultiplexing filtercircuit for separating the frequency band including the f3 and the f4which is obtained by the separation of the first demultiplexing filtercircuit into a frequency band which includes the f3 but none of the f1,the f2 and the f4 practically, and a frequency band which includes thef4 but none of the f1 to the f3 practically, wherein the seconddemultiplexing filter circuit comprises a filter of combination oflow-pass and band elimination filters or a band pass filter as a filterwhere the frequency band including the f2 but none of the f1, the f3 andthe f4 practically is set to be a pass band, and the thirddemultiplexing filter circuit comprises a filter of combination ofhigh-pass and band elimination filters or a band pass filter as a filterwhere the frequency band including the f3 but none of the f1, the f2 andthe f4 practically is set to be a pass band.
 2. The multiplexeraccording to claim 1, wherein the second demultiplexing filter circuitcomprises a low-pass filter as a filter where the frequency bandincluding the f1 but none of the f2 to the f4 practically is set to be apass band, and the third demultiplexing filter circuit comprises ahigh-pass filter as a filter where the frequency band including the f4but none of the f1 to the f3 practically is set to be a pass band. 3.The multiplexer according to claim 1, wherein the first demultiplexingfilter circuit comprises a low-pass filter as a filter where thefrequency band including the f1 and the f2 but neither of the f3 and thef4 practically is set to be a pass band, and a high-pass filter as afilter where the frequency band including the f3 and the f4 but neitherof the f1 and the f2 practically is set to be a pass band.
 4. Themultiplexer according to claim 3, wherein the second demultiplexingfilter circuit comprises a low-pass filter as a filter where thefrequency band including the f1 but none of the f2 to the f4 practicallyis set to be a pass band, and the third demultiplexing filter circuitcomprises a high-pass filter as a filter where the frequency bandincluding the f4 but none of the f1 to the f3 practically is set to be apass band.
 5. The multiplexer according to any of claims 1 to 4, whereinthe multiplexer is formed of a laminated structural body, the laminatedstructural body is constituted so as to include a plurality ofinsulating layers and a patterned conductive layer arranged between theinsulating layers, each of the first demultiplexing filter circuit, thesecond demultiplexing filter circuit and the third demultiplexing filtercircuit includes an inductance component and a capacitance component,and the inductance component and the capacitance component are formed byusing the patterned conductive layer.
 6. The multiplexer according toclaim 5, wherein the insulating layers are made of ceramics.
 7. Themultiplexer according to claim 6, wherein the patterned conductive layeris made of metal.